1. Field of the Invention
The present invention relates to an engine restart control device and, more particularly, to an engine restart control device for a vehicle which has an idle stop function and on which an electric power steering (EPS) system is mounted.
2. Description of the Related Art
There is a vehicle equipped with an engine restart control device including a control means. The control means stops an engine adapted to generate a driving force for running the vehicle when a predetermined stop condition is met and restarts the engine when a predetermined restart condition is met after the stop of the engine.
As an example of such an engine restart control device, there are following ones, for example.
Patent Document 1: Japanese Patent Application Publication No. 2005-271640A
Patent Document 2: Japanese Patent Application Publication No. 2000-345878A
A power steering device for a vehicle according to Patent Document 1 is configured to restart an engine when the change rate of steering torque or the change rate of steering angle of a steering wheel (handle) in an idle stop state exceeds a predetermined threshold.
An engine automatic stop and restart device for a vehicle according to Patent Document 2 is configured to restart an engine when it is determined that a stationary steering operation is carried out on the basis of a steering angle of a steering wheel in an idle stop state.
In this regard, there is a method for detecting the left and right turning of a steering wheel using a steering angle detected by a steering angle detection means (steering angle sensor) or a steering torque detected by a steering torque detection means (torque sensor). However, according to this method, there is a problem that midpoint shift in these detecting means or sensing error in an EPS control means (EPS ECU) of an electric power steering (EPS) system is typically caused. Accordingly, lateral difference in the steering angle of the steering wheel required for restarting an engine may be caused due to the midpoint shift and the sensing error.
Specifically, a vehicle has an idle stop function during stop or an idle stop function during deceleration and a steering torque detection means is equipped with standard on an electric power steering system. In such a vehicle equipped with an engine that can be restarted from an idle stop state when a steering torque detected by the steering torque detection means exceeds a predetermined threshold, a slight steering torque in a left or right direction is detected in an actual steering torque detection means even in a state where a steering torque is not applied to a steering wheel. Further, a sensing error may be caused in an EPS control means of the electric power steering system when sensing a detection signal from the steering torque detection means.
Therefore, a left or right offset (ΔT) is included in the detected sensor torque value. As a result, even when the engine is restarted at the same starting torque threshold (Tres) in the left and right of the steering wheel, there is a difference in the torque required for restarting the engine since a left turning restart torque becomes Tres-ΔT and a right turning restart torque becomes Tres+ΔT. Consequently, there is a problem that lateral difference in the steering angle of the steering wheel required for restarting the engine is caused.